Device for transporting recording media in printers or photocopiers

ABSTRACT

The device for transporting recording media (100), used especially in a fuser station of a printer or photocopier, comprises a counter-roll (201) and a feed roll (205), mounted movably relative to the counter-roll (201), between which rolls the recording medium (100) is transported by friction. Furthermore, a guide bar (214) is arranged in the manner of a balance beam with spacing parallel to the feed roll (205) and so as to be pivotable about an axis of rotation (216) relative to the feed roll (205). In order to press the feed roll (205) against the counter-roll in a force-compensating manner, as required, spring elements (218) are arranged on the guide bar (214) on both sides of the axis of rotation and are coupled to bearing elements (206) of the feed roll (205). The guide bar can be deflected via an adjusting motor (224) for controlling the position of the recording medium (100) between the rolls (201, 205).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device for transporting a recording medium ina printer or photocopier and to the use of a device of this type in afuser station of a printer or photocopier.

2. Description of the Related Art

It is customary to use endless paper with transportation perforations inhigh speed non-mechanical printing apparatuses which operate by theelectrophotographic or magnetic principle. In this case, the endlesspaper is withdrawn from a stack, transported through a transfer stationwith the aid of tractors engaging in the edge perforations and therebycoated with a layer of toner depending on the characters being printed.The layer of toner situated on the recording medium is then thermallyfused in a fuser station, also termed a fixing station. A fuser stationof this type is known, for example, from U.S. Pat. No. 4,147,922. Forthis purpose, the fuser station comprises in a customary manner anelectric, heated fuser, or fixing roller and a feed roller which can bepivoted onto and away from the fuser roller. In this case, the recordingmedium must be guided precisely through the fuser station withoutmovement relative to the fuser roller.

In order to prevent relative movement of this type, it has provednecessary to ensure an even pressing force of the feed roller onto thefuser roller along the length of the roller. With different pressingforces along the length of the roller, there is a risk of the web ofpaper migrating horizontally in the fuser station during the printingoperation. This can lead to tensioning of the web of paper and, withhigh transport speeds, to a tear in the paper.

For the pivoting of a feed roller onto and away from a counter-roller ina fuser station, it is known from German Patent 27 17 260 to arrange thefeed roller on links and to pivot the latter via cam disks. In thiscase, the counter-roller is mounted in a stationary manner.

If the feed roller is not guided and pivoted on precisely parallel tothe counter-roller, different pressing forces act along the rollers.Although the elastic sheathing of the feed roller ensures a certainforce compensation, it has been shown that this force compensation isnot sufficient.

A fusing apparatus for photocopiers is known from European PublishedApplication 0,002,303, which has a fuser roller and a feed roller whichcan be pivoted onto and away from the fuser roller. The feed roller ismounted so as to be pivotable in a support cage, on which an eccentricmember engages. The pressing force of the feed roller onto the fuserroller is measured via an apparatus measuring the deflection of thesupport cage. By pivoting the eccentric, the pressing force of the feedroller along the fuser roller can be changed or adjusted. Pressingfluctuations of the feed roller onto the fuser roller can thus becompensated.

Furthermore, the recording media used can vary in thickness over theirwidth, or the recording media serve as media for credit cards to beprinted, etc.

Additionally, non-mechanical printing apparatuses can be designed insuch a way that they can process webs of recording media of differentwidths. With these, it is necessary to design the fuser station with therollers arranged therein in accordance with the greatest width ofrecording medium. Regions of the fuser roller or of the feed roller inthe fuser station which do not come into contact with the recordingmedium heat up locally more intensely than the actual contact regionswith the recording medium because the recording medium withdraws heatfrom the fuser roller in the fusing region during the fusing operation.This leads to a heat-dependent different diameter of the feed rollerconsisting of elastic material. As a result, the recording medium isdeflected horizontally.

It has therefore proved favorable to monitor the lateral position of therecording medium precisely via a scanning apparatus when it enters thefuser station in order to be able to intervene, if necessary, in termsof control via a control arrangement.

However, the problem of the precise controllable guiding of recordingmedia is not only present wish electrophotographic printers andphotocopiers. Even with other printing apparatuses which operate, forexample, with inking units, it is necessary to position the recordingmedium precisely, at least in the printing region.

For positioning the recording media in printing apparatuses, it iscustomary to use electrically adjustable mechanical guide elements inthe paper duct of the printing apparatus, the scanning of the ACTUALposition of the recording media likewise taking place via mechanicalcontact elements.

For scanning the position of the recording media, it is known from theIBM Technical Disclosure Bulletin, Vol. 23, No. 7a, December 1980 andfrom European Patent 0 031 137 to use optoelectronic scanningapparatuses.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a device fortransporting recording media in printers or photocopiers having a rollerarrangement with a counter-roller and a feed roller and a recordingmedium guided by friction between them, which device is designed in sucha way that the feed roller rests on the recording medium or thecounter-roller with an even pressing force along the length of theroller.

A further aim of the invention is to provide a device in whichpositioning of the recording medium between the rollers is possible.

The device is particularly suitable for installation in a fuser, orfixer, station of an electrophotographic printer or photocopier.

This object is achieved by a device for transporting recording media inprinters or photocopiers having

a) a counter-roller and a feed roller, mounted movably relative to thecounter-roller, between which rollers the recording medium istransported by friction, one of the rollers being driven by an electricmotor,

b) lateral bearing elements for the rollers,

c) a guide bar which is arranged in the manner of a balance bean withspacing parallel to the feed roller and so as to be pivotable about anaxis of rotation relative to the feed roller, and

d) spring elements which are coupled to the guide bar and the bearingelements of the feed roller and are arranged on both sides of the axisof rotation of the guide bar in order to press the feed roller againstthe counter-roller in a force-compensating manner, as required.

Alternately, a fuser station for an electrophotographic printer orphotocopier for thermal fusing of a recording medium, bearing a tonerimage, includes

a) a motor-driven, electrically heated fuser roller and a feed rollerwhich can be pivoted onto and away from the fuser roller, between whichrollers the recording medium is passed for fusing,

b) lateral bearing elements for the feed roller,

c) a guide bar which can be rotated in the manner of a balance beamabout an axis of rotation perpendicular to the longitudinal extent ofthe feed roller, and

d) spring elements, arranged on lateral arms of the guide bar, forforce-compensating pressing of the feed roller onto the fuser roller viathe bearing elements of the feed roller.

Advantageous embodiments of the invention are provided by the devicehaving rotatably mounted links, coupled to the spring elements, havingswivel arms for pressing the feed roller onto the counter-roller.

The device may further include

eccentric elements which are arranged on the links and can be rotatedvia an adjusting motor and that are supported on the bearing elements ofthe feed roller for pivoting the feed roller onto and away from thecounter-roller,

a limiting stop assigned to the links, and

a restoring spring coupled to the bearing elements of the feed roller,the above-mentioned elements being arranged relative to one another insuch a way that, starting from a pivoted-away position, when the feedroller is pivoted on via the eccentric elements counter to the forceeffect of the restoring spring, the links rest on the limiting stop andthus absorb the spring force of the spring elements until the feedroller is supported on the counter-roller.

The eccentric apparatus of the foregoing embodiment may be cam disks.

The guide bar is coupled to an adjusting motor in order to deflect theguide bar about the axis of rotation into predeterminable deflectionpositions and thus to adjust the pressing force of the feed roller ontothe counter-roller along its roller length, according to onedevelopment.

In the foregoing fuser station, links are mounted rotatably about astationary axis of rotation for pressing the feed roller onto the fuserroller via the spring elements.

The fuser station, in one embodiment, may include

eccentric elements which are arranged on the links and can be rotatedvia an adjusting motor and that are supported on the bearing elements ofthe feed roller, for pivoting the feed roller onto and away from thecounter-roller,

a limiting stop arranged in a stationary manner and assigned to thelinks, and

a restoring spring coupled to the bearing elements of the feed roller,the above-mentioned elements being arranged relative to one another insuch a way that, starting from a pivoted-away position, when the feedroller is pivoted on via the eccentric elements counter to the forceeffect of the restoring spring, the links rest on the limiting stop andthus absorb the spring force of the spring element until the feed rolleris supported on the counter-roller.

In the fuser station, the eccentric elements are preferably cams.

One embodiment of the fuser station provides that the guide bar iscoupled to a drive apparatus in order to deflect the guide bar about theaxis of rotation into predeterminable deflection positions and thus toadjust the pressing forces of the feed roller onto the counter-rolleralong its roller length.

By the arrangement of a guide bar which is mounted in the manner of abalance beam and engages with spring elements on the bearing elements ofthe feed rollers, the feed rollers is pressed against the counter-rollerwith an even pressing force over the entire roller length. Any differentpressing forces occurring are compensated. The recording medium is thustransported reliably and without distortion between the rollers.Displacements of the recording medium relative to the rollers areavoided. The device is thus especially suitable for fuser stations inelectrophotographic printers and photocopiers in which a toner image isthermally fused on a recording medium.

In an advantageous embodiment of the device, the force-compensatingeffect can be influenced with the aid of an adjusting apparatus. It isthus possible to control the position of the recording medium betweenthe rollers.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated in the drawings and aredescribed in detail below by way of example.

FIG. 1 is a diagrammatic sectional illustration of a fuser station of anelectro-photographic printing apparatus with the transport devicearranged therein; and

FIG. 2 shows a diagrammatic illustration of the fuser station of FIG. 1with a block circuit diagram of a control arrangement for the lateralpositioning of the recording medium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A printing apparatus operating by the principle of electrophotographycomprises a fuser, or fixer, station for fusing a toner image on therecording medium in the form of an endless web of paper 100. In thiscase, the recording medium 100 is subjected to heat and pressure in thefuser station and a firm bonding of the toner image with the recordingmedium is thus achieved. For thermal fusing, the fuser station comprisesa fuser roller 201 with a heat radiator 202 arranged therein in the formof a halogen lamp. The fuser roller 201 is mounted on a frame 203 of theprinter and is driven via a motor 204. The fuser roller 201 usuallyconsists of a plastic-coated aluminum tube. A feed roller 205 made of asteel tube sheathed in rubber is mounted so that it can be pivoted ontoand away from the fuser roller 201. The feed roller 205 is mounted ontwo lateral bearing elements 206. The bearing elements 206 are mountedin the frame 203 of the printer so as to be pivotable about a stationaryaxis of rotation 207. Arranged for pivoting the feed roller 205 onto andaway from the fuser roller 201 acting as counter-roller are two camdisks 209 which can be rotated via an electric motor 208 (FIG. 2) andrest on guide attachments 210 (rotatable rollers) of the bearingelements 206. Two tension springs 211 engaging laterally on the bearingelements 206 serve as restoring springs for bearing elements 206 andpress the bearing elements 206 against the cam disks 209 via the guideattachments 210. The cam disks 209 are mounted on lever-type links 212with an axis of rotation 213 fixed in the frame 203 of the printingapparatus. Arranged spaced from and parallel to the feed roller is aguide bar 214 which is approximately as long as the feed roller. It ismounted pivotably in a bearing piece 215 approximately in the center ofthe feed roller, specifically about an axis 216 running approximatelyperpendicular to the longitudinal extent of the feed roller. The guidebar 214 has at its ends adjustable attachment elements (adjustingscrews) 217, in which springs 218 connected to the links 212 aresuspended. In conjunction with the centrally mounted guide bar 214, thesprings 218 form a type of balance beam for force compensation of thepressing force of the feed roller 205 onto the fuser roller 201 over thelength of the feed roller. Adjustable stops 219 for the cam disks 209are arranged in the bearing region for limiting the swivel range of thelinks 212. The motor 208 is coupled to the cam disks via across-coupling 220. It allows pivoting of the cam disks 209 about theaxis of rotation 213 corresponding to the direction of the arrowillustrated in FIG. 2 and thus movement relative to the motor 208attached in a stationary manner via attachment elements (screws, etc. )221 to the frame 203 of the printing apparatus.

The spring force of the springs 218 is considerably greater than thespring force of the restoring springs 211 on the feed roller 205. In thepressed-on state (FIG. 1) of the feed roller 205, the links 212 arepivoted away from the stops 219. In accordance with their deflection,cam disks 209 press the feed roller 205 against the fuser roller 201. Inthis case, the pressing force is determined essentially by the springforce of the springs 218 in conjunction with the geometricalconstruction of the link 212 and the degree of deflection of the camdisks 209.

For pivoting away, the cam disks 209 are rotated back via the motor 208.As a result, first the link 212 moves under the effect of the springforce 218 without the feed roller 205 being pivoted away from the fuserroller 201, specifically until the links 212 rest with their lower pivotarms on the stops 219. As a result, the spring force of the springelements 218 is absorbed. On further rotation of the cam disks 219 forpivoting the feed roller 205 away completely, the feed roller 205 isthen raised from the fuser roller 201 under the effect of the restoringspring 211. In this actual pivoting-away operation, the bearing elements206 rest via their attachments 210 on the cam disks 209. Thepivoting-away range and thus the range of rotation of the cam disks 209is limited by an attachment 222 on the cam disks which, with a completerevolution of the cam disks 209, rests on the guide attachments 210 ofthe bearing elements during pivoting-away. The feed roller 205 is thusin the pivoted-away state and the recording medium 100 can be threadedinto the fuser station. The pivoting of the feed roller 205 onto thefuser roller 201 takes place in the opposite direction. In this case,the feed roller 205 is first brought to rest on the fuser roller 201 byrotation of the cam disks 209, specifically counter to the spring forceof the restoring springs 211. On further rotation of the cam disks 209,the links 212 are raised from the stops 219 and the spring force of thesprings 218 is fully effective. The balance beam-type construction ofthe pressing-on mechanism for the feed roller 205 with the guide bar 214and spring elements 218 in conjunction with the links 212 ensures aforce compensation of the pressing force of the feed roller 205 alongthe fuser roller 201 and thus an even fusing force on the recordingmedium 100. This is important for an even fusing result, especially whenrecording media 100 of different widths are used.

As already detailed at the beginning, the fuser station in theelectrophotographic printing apparatus serves for fusing the toner imageapplied to the recording medium in a transfer station onto the recordingmedium 100 by heat and pressure. For this purpose, the recording medium100 shown in FIG. 1 is brought to rest on the fuser roller 201 with itstoner-layer side at the top via a fusing saddle 223 which can be pivotedon and away. It is wrapped around the fuser roller 201 at a wrappingangle Z and is heated up there (pre-heated). The actual fusing thentakes place in a fusing gap, or fixing gap, FX, namely the pressing-onregion between the fuser roller 201 and the feed roller 205. For fusing,the recording medium 100 has to be heated in the fusing regionconsisting of the wrapping angles Z and the fusing gap FX from roomtemperature to a fusing temperature of greater than 110° C. To achieve agood printing quality, it is therefore necessary to guide the recordingmedium 100 precisely in the fuser station.

It is customary to use recording media of different widths or differentformats in electrophotographic printers or photocopiers. In order to beable to guarantee a continuous printing operation, the individualassemblies of the printing apparatus must be designed in such a way thatswitching over between various paper formats or various recording mediawidths is possible without prolonged cooling phases. For this reason,the fuser roller 201 and the feed roller 205 are designed in terms oftheir length for the widest possible recording media format. If arecording medium having a width which is less than the maximum possiblerecording media width is fused between the fuser roller 201 and the feedroller 205, the feed roller 205 is heated locally to a different degree.In the region of the recording medium, the heating is less than in theregion of the feed roller 205 not covered by the recording medium sincethe recording medium absorbs and discharges heat during the fusingoperation.

It has now been established that the different heating of the regions ofthe feed roller in recording media of different widths leads to adifferent expansion of the feed roller. This results in a differentdiameter of the feed roller 205 in the region of the recording mediumand in the region not covered by the recording medium. This leads, inturn, to the recording medium being deflected horizontally in the fusinggap FX. Smearing of the toner image and thus disturbances in the printedimage are the result.

Furthermore, a lateral deflection of this type of the recording mediumleads to tensioning of the recording medium in the paper guides of theprinting apparatuses. In this case, tearing of the paper can be theresult.

It is therefore desirable to control the horizontal position of therecording medium 100 in the fusing gap FX during the fusing operation,specifically especially when recording media of different widths areused. In this case, the positioning itself takes place by changing thepressing force of the feed roller 205 onto the fuser roller 201 over thelength thereof.

A prerequisite for the control is firstly the registration of the ACTUALPOSITION of the recording medium on entry of the recording medium 100into the fuser station in the inlet region of the fusing saddle 223.Arranged there for this purpose is an optoelectronic sensor S whichregisters the lateral position of the recording medium 100 via itstransportation holes. Commercially available optoelectronic scanners oreven mechanical scanning elements or the like can be used as sensors S.

The arrangement illustrated in FIG. 2 for the lateral positioning of theweb-type recording medium 100 comprises a sensor S with an associatedevaluation circuit AS for converting the sensor signals into positionsignals UD. Arranged downstream of the evaluation circuit AS is ananalog-to-digital converter W which converts the position signals UD,supplied by the evaluation arrangement AS, into a digital signal so thatthe latter can be evaluated and processed with the aid of amicroprocessor P. The microprocessor P is connected via a data bus tothe actual control C of the printing apparatus. This control (equipmentcontrol) can be constructed, for example, in accordance with U.S. Pat.No. 4,593,407; a commercially available microprocessor (e.g. Siemens8080 microprocessor) lends itself for use as microprocessor P.Additionally, microprocessor P is connected to a program memory M forreceiving the control program.

The adjusting signals, supplied by the microprocessor P, are amplifiedvia an amplifier AP and fed to the adjusting arrangement E for adjustingthe pressing force of the feed roller 205 onto the fuser roller 201along the fuser roller.

In the exemplary embodiment of FIG. 2, the apparatus E comprises anadjusting motor 224 with an eccentric disk 225 arranged thereon.However, any other adjustable electronic drive apparatus, e.g. asolenoid, is also suitable instead of an adjusting motor. The eccentricdisk 225 is connected to the guide bar 214 via a linkage 226. Byrotating the eccentric disk 225, the guide bar 214 is deflected to avarying extent around the axis of rotation 216 via the linkage 226 andthus the pressing force on the bearing elements 206 of the feed roller205 is changed. The horizontal position of the recording medium can thusbe adjusted in the fusing gap FX.

This adjustment takes place via the arrangement described for thelateral positioning by means of the microprocessor P which compares theACTUAL position signals UD, supplied by the sensor S, with a referenceposition stored, for example, in the memory M and, as a functionthereof, drives the adjusting motor 224 via the amplifier AP. Theposition of the adjusting motor 224, which can be registered, forexample, via a scanning apparatus, is likewise fed to the microprocessorP for evaluation.

The position of the recording medium in the fuser station can beoptimized via the control arrangement. In this case, the aim of controlcan be the so-called zero position of the endless paper, i.e. thepositioning of the transportation perforations of the endless paper on aposition assigned to the position above the dividing line of the sensorsurfaces of the scanner. However, the aim of control can also be lead tothe recording medium if, for example, initially very narrow paper isprinted and then a change to wide paper is envisaged. In this case, thecontrol arrangement takes into consideration the behavior of therecording medium to be expected the future and deflects the recordingmedium at a given time before or after changeover. The differentbehavior of the recording media and any necessary lead can be stored asa program within the memory M of the microprocessor arrangement.

The transport device described in connection with a fuser station of anelectrophotographic printer with a counter-roller and feed roller canalso be used for transporting recording media in other printingapparatuses or copying apparatuses. These recording media can be singlesheets or as webs of endless paper.

If, instead of the tension springs 218, compression springs are used,these engage directly on the lower part of the lever-type links 212 inthe vicinity of the cam disks 209. The stop 219 absorbing the springforce of the spring must be arranged on the upper part of the links 212in an appropriate position.

Furthermore, it is possible, instead of the mechanism described forpivoting the feed roller 205 on and away, to have a simple pivoting-awaylever with a catch mechanism, for example, on the feed roller 205 or todispense completely with the pivoting away. The springs 218 of the guidebar then engage directly on the bearing element 206 of the feed roller205, if they are constructed, for example, as compression springs, orvia pivotable levers corresponding to the lever-type links 212.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

We claim:
 1. A device for transporting recording media in printers orphotocopiers, comprising:a) a counter roller and a feed roller mountedmovably relative to the counter roller, between said rollers therecording medium is transported by friction, an electric motor connectedto drive at least one of the rollers, b) lateral bearing elements onwhich said feed roller is mounted for rotation, means for supportingsaid counter roller for rotation, c) a guide bar mounted as a balancebeam spaced from and parallel to said feed roller and so as to bepivotable about an axis of rotation relative to said feed roller, d)spring elements which are coupled to said guide bar and which bias saidlateral bearing elements of the feed roller and are arranged on eachside of the axis of rotation of said guide bar, and e) means forcoupling said spring elements to said feed roller in order to press thefeed roller against the counter roller in a force-compensating manner.2. A device as claimed in claim 1, wherein said means for couplingcomprisesrotatably mounted links coupled to said spring elements andhaving swivel arms for pressing said feed roller onto said counterroller.
 3. A device as claimed in claim 2, further comprising:eccentricelements mounted on said rotatably mounted links, an adjusting motorconnected for rotating said eccentric elements and said eccentricelements bearing on said bearing elements of said feed roller forpivoting said feed roller onto and away from said counter roller, alimiting stop mounted to selectively abut said rotatably mounted links,and a restoring spring coupled to said bearing elements of said feedroller so that, starting from a pivoted-away position, when said feedroller is pivoted via said eccentric elements counter to a force effectof said restoring spring, said rotatably mounted links rest on saidlimiting stop and thus absorb spring force of said spring elements untilsaid feed roller is supported on said counter roller.
 4. A device asclaimed in claim 3, wherein said eccentric elements include cam disks.5. A device according to claim 1, further comprising:an adjusting motorcoupled to said guide bar in order to deflect said guide bar about theaxis of rotation into predeterminable deflection positions and thus toadjust pressing force of said feed roller onto said counter roller alongits roller length.
 6. A fuser station for an electrophotographic printeror photocopier for thermal fusing of a recording medium bearing a tonerimage, comprising:a) a motor-driven, electrically heated fuser rollerand a feed roller which is mounted to be pivotable onto and away fromsaid fuser roller, between said rollers the recording medium is passedfor fusing, b) lateral bearing elements on which said feed roller isrotatably mounted, c) a guide bar mounted to be rotated as a balancebeam about an axis of rotation perpendicular to a longitudinal extent ofsaid feed roller, and d) spring elements connected to lateral arms ofsaid guide bar and having means for force-compensating pressing of saidfeed roller onto said fuser roller via said bearing elements of saidfeed roller.
 7. A fuser station as claimed in claim 6, furthercomprising:links mounted rotatably about a stationary axis of rotationso as to press said feed roller onto said fuser roller via said springelements.
 8. A fuser station as claimed in claim 7, furthercomprising:eccentric elements connected on said links and rotatable viaan adjusting motor and bearing against said bearing elements of saidfeed roller for pivoting said feed roller onto and away from saidcounter roller, a limiting stop mounted in a stationary position andselectively abutting said links, and a restoring spring coupled to saidbearing elements of said feed roller so that, starting from apivoted-away position, when said feed roller is pivoted via saideccentric elements counter to a force effect of said restoring spring,said links rest on said limiting stop and thus absorb a spring force ofsaid spring element until said feed roller is supported on said counterroller.
 9. A fuser station as claimed in claim 8, wherein said eccentricelements comprise cams.
 10. A fuser station as claimed in claim 6,further comprising:a drive apparatus to which said guide bar is coupledin order to deflect said guide bar about the axis of rotation intopredeterminable deflection positions and thus to adjust pressing forcesof said feed roller onto said counter roller along its roller length.